化學機械研磨機對複晶矽氧化層之應用

Abstract

使用化學機械研磨機(CMP)研磨複晶矽層表面，可使其表面比一般複晶矽 層表面平坦，這可用掃描式探針顯微鏡(AFM)觀察得到。從經由研磨的複 晶矽層熱氧化所得到的複晶矽氧化層，有較低的漏電流和較高的崩潰電壓 ，這可適用於非揮發性記憶元件。相較於一般的複晶矽氧化層，我們還發 現它可獲得較低的電子捕捉速率(electron trapping rate)和較高的崩潰 電荷密度(charge to breakdown)，甚至在正閘極偏壓時，它的崩潰電荷 密度是一般複晶矽氧化層的10倍以上。其捕捉的電子數量減少很多而且大 部份分布在複晶矽氧化層的上半部。這裡也研究低壓氣相沉積系統( LPCVD)沉的複晶矽氧化層之特性，因為氧化層和複晶矽層界面的表面平坦 度並沒有變差，所以其氧化層有較佳的絕緣特性。這種經由研磨處理的低 壓氣相沉積複晶矽氧化層展現極佳的電性，其中值得一提的是對200(厚度 的複晶矽氧化層，當正閘極偏壓時，其崩潰電荷密度可達到6庫倫/平方公 分。 The surface of the polysilicon film polsihed with CMP is smoother than that of the unpolished poysilicon film and they are observed by AFM. The polyoxide grown thermally from the polished polysilicon film has a lower leakage current and a higher breakdown electric field, which are suitable for the nonvolatile memory application. Comparing to conventional polyoxide, a lower electron trapping rate and a larger charge to breakdown(Qbd) are found in the polished sample. Furthermore, the Qbd of the polished samp is much larger (>10x) than that of the unpolished sample under +Vg stress. The trapped charges of the polished sample almost locate at the upper portion of polyoxide and are much reduced. This work also reports on the characteristics of the LPCVD-stacked polyoxide. It exhibit a better dielectric propertiy because the roughness of polyoxide/ poly-1 doesn't enhance during the formation of polyoxide. The characterisitcs of the polished sample are much better than those of the unpolished sample. By the way, forhe 200( thick polyoxide, the Qbd of the polsihed sample is as high as 6 C/cm2 under +Vg stress.